The present disclosure relates to implantable electronic devices and systems, and to temperature detecting strategies employed in conjunction with such devices.
Implantable electronic devices and systems, such as stimulators, can create a stimulus that is transferred to the nerves and tissues of a patient's body in order to treat a variety of biological disorders. Tissues can be stimulated directly or indirectly to elicit a desired response. Direct stimulation involves the provision of one or more stimuli directly to the stimulated tissue while indirect stimulation involves the provision of one or more stimuli to adjacent or otherwise related tissue, where the related tissue causes the desired response to be elicited from the stimulated tissue. The desired response can be inhibitory or excitatory. Inhibitory responses tend to discourage certain behavior by the stimulated tissue, whereas excitatory responses tend to encourage certain behavior by the stimulated tissue. Encouraged or discouraged behaviors can include cellular depolarization, the release of chemical species, and/or the inhibition of cellular depolarization. Tissue can be stimulated, e.g., using electrical, chemical, thermal, electromagnetic, and/or mechanical stimuli.
For example, pacemakers can be used to treat cardiac arrhythmia, defibrillators can be used to treat cardiac fibrillation, cochlear stimulators can be used to treat deafness, retinal stimulators can be used to treat blindness, muscle stimulators can be used to treat paralysis in limbs, spinal cord stimulators can be used to treat chronic pain, cortical and deep brain stimulators can be used to treat motor and psychological disorders, and other neural stimulators can be used to treat disorders such as urinary urge incontinence, sleep apnea, and sexual dysfunction.
As there are a number of different applications, there are similarly varying types of implantable electronic devices and systems. For example, a spinal cord stimulator can be used to treat chronic pain, while a microstimulator can be used to treat disorders such as urinary urge incontinence, sleep apnea, or sexual dysfunction. As such, the design and location of the implantable electronic device can vary with the nature of the application for which it is used. Additionally, the manner in which the device operates can vary with the nature of the application. For example, pain management applications can necessitate the use of more powerful stimulation than the treatment of cardiac arrhythmia or more frequent stimulation than sexual dysfunction applications. Moreover, some patients will require higher power or more frequent stimulation than others, and will therefore also consume more power than other patients with similar devices. As such, the requirements directed to a power source associated with an implantable electronic device also may vary in accordance with the specific patient and application.
Regardless of the application and the individual requirements, however, implantable electronic devices and systems require power from some source to provide the electrical stimulus and to control their own operation. The power source associated with the implantable electronic device can be external to the patient, such as an alternating current power supply. An external power source, however, must be connected to the device in order to deliver power, such as through transcutaneous wires or inductive coupling via an electromagnetic field. Alternatively, the power source can be internal to the patient, such as a battery or a capacitor.
Because an implantable electronic device typically is intended for long-term treatment, it is desirable for the implanted device to operate for an extended period of time. However, devices powered by a primary (non-rechargeable) battery have a finite lifetime and must be surgically removed and replaced when the primary battery is at or near the end of its useful life. Surgical replacement of the power source or the implanted device, however, is not acceptable in many applications.
Where a battery is used as the power source for an implanted electronic device, the battery must have sufficient storage capacity to allow the device to operate for a reasonable length of time. For low-power devices, such as cardiac pacemakers, a primary battery can have an operational life of up to ten years. Implantable electronic devices designed for use in other applications, such as spinal cord stimulators, can demand much greater amounts of power due to higher stimulation rates, pulse widths, or stimulation thresholds. If a primary battery was employed to power such devices, it would require a much larger storage capacity in order for the device to operate for a reasonable length of time. Unfortunately, the amount of additional storage capacity required could result in a device form factor that is too large to implant comfortably or practically within a patient.
Some implantable electronic devices and systems have been designed to use a secondary (rechargeable) battery as the power source, allowing the power stored in the batteries to be periodically replenished through a device charging operation. Thus, a patient with a device powered by a secondary battery can be free of cumbersome external devices and is only required to periodically recharge the power source. The use of a rechargeable battery in an implantable electronic device is described in U.S. Pat. No. 6,553,263, incorporated herein by reference.
The process of recharging the power source associated with an implantable electronic device typically requires close attention by the caregiver or the patient, however. For example, the temperature of the implanted device should not be allowed to rise above a certain threshold during the device charging operation, as a temperature increase in an implanted device can cause the temperature of the surrounding tissue to rise as well.